The present invention is related to the field of printing, and in particular, to a method and an apparatus for clamping flexible plates of different thickness and format onto an imaging cylinder, e.g., for exposure in a computer-to-plate imaging device by light energy according to imaging data.
Flexographic plates are frequently exposed from computer data using computer-to-plate (CTP, C2P) imaging. Mounting such plates on a cylinder, e.g., the cylinder or drum of an external drum imaging device is recognized as a problem. For example, one method to mount a flexographic plate on a cylinder is to fix the plates with adhesive tape at the edges. More modern methods use a clamping bar, which clamps the top and bottom edge of a full-size flexographic plate onto the cylinder. First adhesive tape method is very time consuming and second method using a clamping bar only works with full format plates. Since flexographic plate material is relatively expensive a modern method to mount partial plates on a full format cylinder are becoming more and more important.
An example of an external drum imaging device for which such a method and apparatus is applicable is the Esko-Graphics Cyrel Digital Imager (CDI) made by Esko-Graphics A/S, Ballerup, Denmark, the assignee of the present invention.
There is a need in the art for an economical easy-to-use method and apparatus to mount plates of different thickness and format directly onto the imaging cylinder.
In this description and in the claims, by a full-format plate is meant a plate that covers the whole imaging area of the cylinder. By a partial-format plate is meant a plate that covers part of the overall imaging area, such that several partial-format plates (also called plate segments) may be combined to cover the whole imaging area.
One prior art method is for a machine operator to manually mount a full-format plate or partial-format plates onto a cylinder with adhesive tape. Such a method is used, for example, by external drum imaging machines such as the ThermoFlex™ product line made by CREO Inc. of Burnaby, BC, Canada. However, to mount full-format or partial-format plates with adhesive tape is highly time consuming, the operator first mounts a first edge of the plate on the cylinder, fixes it with adhesive tape, turns the cylinder around so that the plate covers the cylinder, and then tapes all the rest of the edges of the plate.
Another prior art solution is for the machine operator to mount full-format plates—those that fully cover the circumference of a cylinder—with the use of a clamp, which is activated manually. An example of a device for so mounting full-format plates is a device used with an imaging drum, called EasyClamp™, made by Esko-Graphics A/S, Ballerup, Denmark, the assignee of the present invention. If partial-format plates are used, the machine operator first mounts partial-format plates onto the cylinder with the use of adhesive tape. The mounting by use of adhesive tape, as stated above, is time consuming.
Yet another prior art solution is for the machine operator to mount full-format plates—the case of the circumference of the cylinder being fully covered by the plate—using a terminal strip, which is activated manually. For mounting a plate, the terminal strip has to be opened manually, the plate has to be fixed under the terminal strip, the terminal strip has to be closed manually, the cylinder then has to be turned around, the terminal strip has to be opened manually again, the second plate edge has to be positioned under the terminal strip and then the terminal strip has to be closed manually. In all cases with the use of a terminal strip, the activation is done by manually by turning a key. This method is suggested, for example, in the HelioFlex® range of products made by HELL Gravure Systems GmbH of Kiel, Germany.
Note that as is the case with the Esko-Graphics EasyClamp™, the terminal strip is only for full-format plates. The machine operator mounts partial-format plates with the use of adhesive tape. The mounting by use of adhesive tape, as stated above, is time consuming.
There thus is a need in the art for a method and apparatus that avoids the manual steps of opening and closing clamping devices or a terminal strip, and for an apparatus therefore.
There further is a need in the art for a imaging cylinder that includes a plurality of clamping devices, positioned in a respective plurality of different axial positions, in a respective plurality of different circumferential positions, and/or in a respective plurality of both different axial and different circumferential positions, in order to avoid having to use adhesive tape to fix a partial-format plate to a imaging cylinder.
Thus both partial and full-format plates can be directly clamped at the end edges by the clamping device.
There also is a need in the art to automatically clamp a flexible plate automatically on a imaging cylinder.
There have been previous attempts at automating plate clamping. For example, U.S. Pat. No. 106,561,094 titled “DEVICE FOR FIXING A FLEXIBLE PLATE ON A IMAGING CYLINDER” and U.S. Pat. No. 106,598,530 titled “METHOD FOR FASTENING A FLEXIBLE PLATE,” both assigned to Koenig & Bauer AG, of Würzburg, Germany, describe some such other attempts. These are referred to herein as the Koenig & Bauer methods and mechanisms, as the case might be.
The Koenig & Bauer clamping mechanisms are relatively complicated and more expensive. Therefore there is still a need in the art for new clamping methods, e.g., that are simpler and less expensive than the Koenig & Bauer methods and mechanisms.
The Koenig & Bauer methods are applicable to flexible plates that have bent suspension legs. Typical flexographic plates need to be clamped at the end edges, and such do not typically have bent suspension edges. Therefore there still is a need in the art for clamping both full-format and partial-format flexible plates at the end edges, such plates not having bent suspension edges.
The patents describe the use of automatic loading in imaging cylinders; the present invention related to loading on imaging cylinder for CTP systems.
The Koenig & Bauer methods and apparatuses limit the number of clamps on the peripheral cylinder surface to two. Therefore there still is a need in the art for a clamping method and clamping apparatuses such that the number of clamping devices on a cylinder is not limited to a relatively small number.
There further is a need in the art for integrating a mechanism into an imaging cylinder to clamp and release flexible plates. There further is a need in the art for a clamping mechanism and clamping method that can work for a relatively large number of plate formats and thicknesses.